This application claims the priority of Japanese Patent Application No. 11-042842 filed on Feb. 22, 1999, which is incorporated herein by reference.
The present invention relates generally to a transmission which includes shift forks for activating clutches selectively to establish power transmission through speed change gear trains, and particularly to a gearshift which conveys a force applied by a shift lever to a shift fork appropriate for activating a target clutch.
In general, such gearshifts are used in manual shift transmissions. When the driver manipulates the shift lever for a desired gear change, a force applied to the shift lever is conveyed to a shift fork which activates a corresponding clutch (for example, a synchromesh type clutch) in the gearshift. In the gearshift, a plurality of speed change gear trains are disposed parallel with one another and rotationally between two shafts which are provided parallel with each other, and a plurality of clutches are provided each for a corresponding gear train, on one of the shafts.
In such a transmission, the number of available speed change ratios corresponds to the number of gear trains which are available for speed change, and a clutch and a shift fork are disposed close to each of the speed change gear trains. Typically, a transmission is equipped with a certain number of speed change ratios to satisfy the performance need of a vehicle which incorporates the transmission. Recent years, transmissions have been required to have a large number of speed change ratios to improve the driving characteristics of vehicles. For a transmission to have a large number of speed change ratios, it must have the corresponding numbers of clutches and shift forks. Because of design limitations for layout and strength, the clutches tend to be disposed away from one another in the transmission, and the shift forks are also disposed away from one another accordingly. If the shift forks are disposed apart from one another, then a mechanism which conveys the force applied by the shift lever to the respective shift forks must be extended to the positions where the shift forks are located in the transmission. However, such extension is a disadvantage because the shifting force conveying mechanism incorporated in the gearshift becomes complex in design.
The directions and pattern of the movements of the shift lever are determined to facilitate the manageability of the shift lever by the driver. On the other hand, the direction of the movement of each shift fork is determined consequently to the layout of the gear trains and the clutches whose positions are determined to secure sufficient strength as mentioned above. Therefore, the directions of the movements of the shift lever does not necessarily match the directions of the movements of the shift forks. Therefore, in some cases, the shifting force conveying mechanism of the gearshift includes a rocking lever, which functions to reverse the direction of the shifting force applied by the shift lever, to convey the force to a target shift fork (for example, refer to Japanese Laid-open Patent Publications No. H8 (1996) -14385 (A) and No. H9 (1997) -250635 (A)).
Many prior-art transmissions had only one such rocking lever, so the layout of the rocking lever was relatively easy and simple. However, as transmissions have acquired an increased number of speed change ratios, requiring an increased number of clutches, recently, a plurality of rocking levers are now necessary. In this case, because each rocking lever must be provided to a corresponding linkage which conveys the shifting force independently, there is a problem that the design of a gearshift which incorporates a plurality of rocking levers tends to become complicated.
To solve the above mentioned problem, the present invention presents a gearshift which includes a plurality of rocking levers, yet whose design is relatively simple.
It is another object of the present invention to provide a gearshift which enables a plurality of rocking levers to be assembled and incorporated therein relatively easily and thereafter be retained there securely.
The present invention provides a gearshift for a transmission which incorporates a plurality of speed change gear trains ( e.g., the LOW, SECOND, THIRD, FOURTH, FIFTH, SIXTH and REVERSE gear trains of the embodiment described in the following section), a plurality of clutch means (e.g., the LOW, SECOND, THIRD, FOURTH, FIFTH, SIXTH and REVERSE clutches of the following embodiment) to select one of these gear trains for power transmission, and a plurality of shift forks ( e.g., the LOW or SECOND shift fork 73, the THIRD or FOURTH shift fork 57, the FIFTH or SIXTH shift fork 58 and the REVERSE shift fork 76 of the following embodiment). This gearshift, which coveys the force applied by a shift lever to the shift forks selectively to achieve a gear change, comprises a plurality of linkages which convey the force applied by the shift lever to the shift forks selectively. In this gearshift, at least two of the linkages include rocking levers (e.g., the LOW or SECOND rocking lever 65 and the REVERSE rocking lever 66 of the following embodiment), respectively, each of which functions to reverse the direction of the force applied by the shift lever. These rocking levers are disposed on a common pivot ( e.g., the retaining pin 67 of the following embodiment), such that each rocking lever can swing independently thereon.
A gearshift according to the present invention is useful especially for a transmission whose clutches are disposed apart from one another because of a design limitation inevitable for incorporating a large number of speed change ratios. The shifting force applied by the shift lever is conveyed securely and selectively through a plurality of rocking levers to the shift forks which activate the corresponding clutches. Because the rocking levers are disposed each independently pivotable on a common pivot, the mounting of the rocking levers is simple. Therefore, the gearshift itself can be assembled relatively easily, and its construction can be made simple and compact.
It is preferable that these rocking levers include smooth contact surfaces (e.g., the contact surfaces 65c and 66c of the following embodiment) near the pivot where the rocking levers meet one another in sliding contact. In this construction, the rocking levers disposed next to one another can swing independently and smoothly around the pivot, each rocking lever sliding on the other rocking levers with the smooth contact surfaces, as it swing independently from the others. These contact surfaces are provided only near the pivot to make the contact areas small to minimize friction and to maximize the ease of sliding. Furthermore, because the matching of the contact surfaces of the rocking levers is visually and easily confirmable during assembly, the rocking levers can be assembled in their correct orientation without being positioned in any wrong way.
Preferably, the rocking levers in plurality, which are disposed next to one another and are capable of swinging around the pivot, be disposed such that one ends of the rocking levers engage lever side members ( e.g., the LOW or SECOND shift rod 51 and the REVERSE shift piece 64 of the following embodiment) which are connected to and movable by the shift lever in the axial direction of the transmission while the other ends of the rocking levers engage fork side members (e.g., the engaging member 72 of the LOW or SECOND shift fork shaft 71 and the REVERSE shift fork shaft 75 of the following embodiment) which are connected to and movable with the shift forks in the axial direction of the transmission. In this case, it is preferable that at least one ends or the other ends of the rocking levers be retained between the lever side members or between the fork side members, at the lateral outsides of the rocking levers in the axial direction of the pivot.
In this construction, the upper ends and the lower ends or at least one ends of the rocking levers, which are disposed next to one another, are sandwiched securely between the lever side members and/or between the fork side members, with the rocking levers being still capable of swinging. Therefore, the rocking levers, which are sandwiched at least at one ends thereof, are maintained there, securely without dislocation.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.